الفهرس 
Basic Concept of Multilevel Database SecurityOnly 14 pages are availabe for public view
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Abstract
Multilevel database security is based on the Bell-LaPadula model [1], which is stated in terms of subjects and objects. A subject is an active entity, such as a process that can request access to objects, whereas an object is a passive entity, such as a record, a file, or a field within a record. Every subject is assigned a clearance level and every object a classification level. Access levels are used to govern access control in MLS databases based on the following three rules:
1- A user can read data which has security level equal to or lower than his security level (The simple security property).
2- A user can write data which has security level equal to or higher than his security level (The *-Property).
3- A user can write data which has security level equal to his security level (The Strong * property).
The major difference between a conventional database and a multilevel secure database is that the conventional one has only single level of data. Authorized users of the conventional database are allowed to have access to the same data. MLS database, on the other hand, has several security clearance levels for the users and security labels for data objects such as files, records or fields.
This thesis focuses on designing a proposed encryption-based multilevel database model by adding an encryption algorithm to the Multilevel Relation (MLR) model and implementing a prototype using Microsoft SQL server database for studying the performance of the proposed model and the impact of applying the encryption on multilevel database security. Also it presents a formal model for
IV
the DML operations like SELECT, INSERT, UPDATE and DELETE in the proposed encryption-based multilevel database model and give the mathematical proofs of soundness, completeness, and security for the DML operations of the proposed model. The mathematical proofs show that the DML operations transform any legal database state to a legal database state which indicates the powerful of the proposed encryption-based multilevel database model. The work presented in this thesis offers several major contributions to the field which include:
1- Adding encryption system as additional security layer over the multilevel security layer for the database which provides high level of security and robustness against database attacks.
2- Reducing the multilevel database size by removing the attributes classification columns and encrypting the record by an encryption key according to its security level (Tuple Classification).
3- Reducing the complexity of the design the multilevel database security by making the database designer do not need to create additional columns for attributes classification.
4- Implementing a prototype to be used to perform a series of experiments to measure the performance cost for applying encryption in multilevel database security.
5- Redefining the mathematical model for the DML operations for multilevel database security to support the new encryption system.
6- Showing the mathematical proofs of soundness, completeness, and security for the proposed model.